If it were my wife, and i wanted to feel the most confident with her being able to defend herself, i would more than likely go with a blade oriented system such as Kali/Silat. IMHO it makes for better awareness, sensitivity, addresses a more realistic approach to combat, and is effective no matter what your age, size, shape, or gender. I would also add in elements of Kino Mutai, Muay Thai, and BJJ, but blending them into the Kali mindset of combat, not sport.